The effects of free Cys residues on the structure, activity, and tetrameric stability of mammalian uricase.

Mammalian uricases contain four conserved cysteine (Cys) residues, but little is known about their structures and functions. In this study, we first confirmed that all four Cys residues are free and not involved in disulfide bond formation, using canine uricase as a model protein. Cys residues had a greater effect on stability than on activity based on single Cys-to-Ser (serine) substitutions. Circular dichroism (CD) and homology modeling indicated that C188S reduces ß-sheet contents and inter- and intra-subunit hydrophobic interaction, potentially impairing the core tetrameric ß-barrel structure of the tunneling-fold protein, and ultimately decreased the tetrameric stability. Additionally, the inactivation of C188S during the stability tests may be a complex process involving depolymerization followed by irregular aggregation. Double mutations or thiol blockage of Cys188 and Cys195 significantly disrupted the formation and stability of tetrameric uricase, which may be mediated by the free thiols in Cys residues. The present results demonstrated that the free Cys residues are essential for tetrameric formation and stability in mammalian uricase. This implies that free cysteine residues, although not involved in disulfide bonding, may play important structural roles in certain proteins, underscoring the significance of the hydrophobic characteristics of the free thiols in Cys residues. KEY POINTS: • Four Cys residues are not involved in disulfide bonding in mammalian uricase. • The hydrophobicity of free thiols is critical for tetrameric stability in uricase. • Free Cys residues can serve structural roles without involving in disulfide bonds.

Preparation of Conotoxin-Encapsulated Chitosan Nanoparticles and Evaluation of Their Skin Permeability.

µ-Conotoxin CnIIIC (conotoxin, CTX)-loaded chitosan nanoparticles (CTX-NPs) were prepared using the ionic cross-linking method. The CTX-NPs were spherical and well with a polydispersity index of 0.292 ± 0.039, drug loading efficiency of 25.9 ± 1.2%, and encapsulation efficiency of 95.6 ± 1.3%. In vitro release studies showed that the release behavior of CTX-NPs in a pH 5.0 acetate buffer followed zero-order kinetics. In vitro transdermal experiments using Franz diffusion cells mounted with mouse abdominal skin demonstrated that the cumulative intradermal deposition amount of CTX per unit area in 8 h (D8) and permeability coefficient (Pf) of CTX loaded on CTX-NPs were 2.30- and 7.71-times that of the CTX solution. In vivo transdermal experiments in mice showed that the amount of CTX deposited in the skin after 8 h of CTX saline administration was significantly lower than that of CTX deposited in the skin after administration of CTX-NPs. In vitro fluorescence labeling transdermal studies through Franz diffusion cells mounted with mouse abdominal skin indicated that CTX-NPs aggregated at hair follicles. Skin irritation tests in mice indicated that the irritation due to CTX-NPs was negligible. The cytotoxicity experiment showed that the viability of Balb/c 3T3 cells with CTX-NPs containing 230 µg/mL (0.08 µM) CTX was greater than 75%. CTX-NPs increase intradermal deposition of CTX by accumulating in hair follicles, which has positive implications for transdermal penetration of CTX.

The Effects of Cadmium Exposure on Fitness-Related Traits and Antioxidant Responses in the Wolf Spider, Pardosa pseudoannulata.

The objective of the present study was to assess the ecotoxicological responses of Pardosa pseudoannulata to a common environmental pollutant, cadmium. Third-instar spiderlings and adult spiders were exposed to sublethal concentrations of CdCl2 solution in their drinking water. The Cd content in P. pseudoannulata adults increased significantly with the number of days of exposure to a 0.2 mM CdCl2 solution, when exposed to 2 mM CdCl2 solution, the Cd content in the spiders increased sharply in the first two (male) or three (female) weeks, and then no significant changes were recorded following with the next three (male) or two (female) weeks exposure. Exposure of spiders to Cd contaminated drinking water resulted in reduced body mass, delayed development, fewer eggs and increased mortality. Significantly higher activities of superoxide dismutase, catalase and glutathione-S-transferase were recorded in the spiders after 7 day exposure to 0.2 mM CdCl2 solution. However, longer-term exposures or increased Cd concentrations did not result in significantly higher antioxidant enzyme activity relative to control treatment.

Males armed with big weapons win fights at limited cost in ant-mimicking jumping spiders.

A core assumption of sexual selection theory is that sexually selected weapons, specialized morphological structures used directly in male contests, can improve an individual's reproductive success but only if the bearer can overcome associated costs, the negative effects on the bearer's fitness components. However, recent studies have shown that producing and wielding exaggerated weapons may not necessarily be costly. Rather, some traits can be selected for supporting, or compensating for, the expense of producing and wielding such exaggerated weapons. In the ant-mimicking jumping spider Myrmarachne gisti, exaggerated chelicerae are borne only by adult males and not females, showing sexual dimorphism and steep positive allometry with body size. Here, we determine the potential benefits of bearing exaggerated chelicerae during male contests and explore the potential for costs in terms of prey-capture efficiency and compensation between chelicera size and neighboring trait size. While males with longer chelicerae won most of their male-male contests, we found no significant differences in prey-capture efficiency between males and females regardless of whether prey was winged or flightless. Males' elongated chelicerae thus do not impede their efficiency at capturing prey. Furthermore, we found that the sizes of all neighboring traits are positively correlated with chelicera size, suggesting that these traits may be under correlational selection. Taken together, our findings suggest that M. gisti males armed with the exaggerated chelicerae that function as weapons win more fights at limited cost for performance in prey capture and compensate for neighboring structures.

Two-Dimensional Graphene-Based Potassium Channels Built at an Oil/Water Interface.

Graphene-based laminar membranes exhibit remarkable ion sieving properties, but their monovalent ion selectivity is still low and much less than the natural ion channels. Inspired by the elementary structure/function relationships of biological ion channels embedded in biomembranes, a new strategy is proposed herein to mimic biological K+ channels by using the graphene laminar membrane (GLM) composed of two-dimensional (2D) angstrom(Å)-scale channels to support a simple model of semi-biomembrane, namely oil/water (O/W) interface. It is found that K+ is strongly preferred over Na+ and Li+ for transferring across the GLM-supported water/1,2-dichloroethane (W/DCE) interface within the same potential window (-0.1-0.6 V), although the monovalent ion selectivity of GLM under the aqueous solution is still low (K+/Na+~1.11 and K+/Li+~1.35). Moreover, the voltammetric responses corresponding to the ion transfer of NH4+ observed at the GLM-supported W/DCE interface also show that NH4+ can often pass through the biological K+ channels due to their comparable hydration-free energies and cation-π interactions. The underlying mechanism of as-observed K+ selective voltammetric responses is discussed and found to be consistent with the energy balance of cationic partial-dehydration (energetic costs) and cation-π interaction (energetic gains) as involved in biological K+ channels.

Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider.

In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings (BDs) in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic BDs in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders; therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among BDs, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans, in particular, were attracted to BDs at a higher rate than to spiders, other dipterans and hymenopterans were attracted to BDs at a similar rate as to spiders. Both spiders and BDs attracted insects at a significantly higher rate than did control leaves. As predicted, prey was attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and BDs can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured by spiders may misidentify them as BDs, and bird-dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P. ceylonica.

Conspicuous cruciform silk decorations deflect avian predator attacks.

Although camouflage as an effective antipredator defense strategy is widespread across animals, highly conspicuous color patterning is not uncommon either. Many orb-web spiders adorn their webs with extra bright white silk. These conspicuous decorations are hypothesized to deter predators by warning the presence of sticky webs, camouflaging spiders, acting as a decoy, or intimidating predators by their apparent size. The decorations may also deflect predator attacks from spiders. However, empirical evidence for this deflection function remains limited. Here, we tested this hypothesis using the X-shaped silk cruciform decorations built by females of Argiope minuta. We employed visual modeling to quantify the conspicuousness of spiders and decorations from a perspective of avian predators. Then, we determined actual predation risk on spiders using naïve chicks as predators. Spider bodies and decorations were conspicuous against natural backgrounds to the avian visual systems. Chicks attacked the spider main bodies significantly less frequently on the decorated webs than on the undecorated webs, thus reducing predation risk. When both spiders and decorations were present, chicks also attacked the spider main bodies and their legs or decorations, and not randomly: they attacked the legs or decorations sooner and more frequently than they attacked the main bodies, independent of the ratio of the surface area between the decoration and spider size. Despite the increase in detectability, incorporating a conspicuous cruciform decoration to the web effectively defends the spider by diverting the attack toward the decoration or leg, but not by camouflaging or intimidating, thus, supporting the deflection hypothesis.

UVB-based mate-choice cues used by females of the jumping spider Phintella vittata.

Although there are numerous examples of animals having photoreceptors sensitive to UVA (315-400 nm) [1] and relying on UVA-based mate-choice cues [2-5], here we provide the first evidence of an animal using UVB (280-315 nm) for intraspecific communication. An earlier study showed that Phintella vittata, a jumping spider (Salticidae) from China, reflects UVB [6]. By performing six series of binary mate-choice experiments in which we varied lighting conditions with filters (UVB+ [no filter] versus UVB-, UVB+ versus ND1, UVB+ versus ND2, UVB- versus ND1, UVB- versus ND2, and UVB- versus UVA-), we show that significantly more UVB + males than UVB- males are chosen by females as preferred mates. Female preference for UVB-reflective males is not affected by differences in brightness or by UVA.

Three new species of the segmented spider genus Qiongthela (Mesothelae, Liphistiidae) from Hainan Island, China.

We report three new species of the segmented trapdoor spider genus Qiongthela Xu & Kuntner, 2015 collected from Hainan Island, China based on morphological characters: Q. dongfang sp. nov. (♂♀), Q. nankai sp. nov. (♂♀), Q. yalin sp. nov. (♂♀). We also provide the GenBank accession codes of the DNA barcode gene, cytochrome c oxidase subunit I (COI), of the type specimens of all three new species to aid future identification.

Four new species of the primitively segmented spider genus Qiongthela from Hainan Island, China (Mesothelae, Liphistiidae).

The primitively segmented spider genus Qiongthela Xu & Kuntner, 2015 consists of seven species that are distributed in Hainan Island, China and southern Vietnam. Of the seven species, five are known from Hainan Island. In this study, four more Qiongthela species collected from Hainan Island are diagnosed and described as new to science based on morphological characters: Q. baoting sp. nov. (♂♀), Q. qiongzhong sp. nov. (♂♀), Q. sanya sp. nov. (♂♀), Q. yinggezui sp. nov. (♂♀). To facilitate future identification, the GenBank accession codes of the DNA barcode gene, cytochrome c oxidase subunit I (COI), for all the type specimens are also provided.

Influence of maternal diet on offspring survivorship, growth, and reproduction in a sheetweb spider.

Prey vary dramatically in quality, and maternal diet is generally assumed to substantially influence offspring survivorship, growth, and reproduction in spiders. Numerous studies that have tested this hypothesis have focused exclusively on parental generation or have considered relatively few fitness components of juvenile offspring. However, maternal diet may have a substantial effect on fitness performance beyond juvenile offspring. Here, we investigated the influence of one-time maternal feeding on multiple offspring fitness components, including the survival rate and growth of juvenile offspring as well as the mating and reproductive success of adult offspring in Hylyphantes graminicola, a sheetweb spider with an extremely short lifespan (∼1 month). We fed field-collected adult female spiders two different diets only once immediately before oviposition: midges (Tendipes sp.) only (MO) or flies (Drosophila melanogaster) only (FO). Juvenile offspring of MO females had significantly higher survival rate, faster growth, and larger male size at maturity than FO offspring. Although maternal diet did not significantly influence mating behavior or fecundity of female offspring overall, those of MO females laid eggs earlier and their eggs also hatched earlier and had a higher hatching rate than those of FO females. Intriguingly, one-time maternal feeding was sufficient to have such an influence on offspring fitness even beyond juvenile offspring in Hgraminicola This one-time maternal effect may be widespread in other spiders and other invertebrates with a short lifespan.This article has an associated First Person interview with the first author of the paper.

Four new species of the trapdoor spider genus Conothele Thorell, 1878 (Araneae, Halonoproctidae) from China.

Herein four species of the trapdoor spider genus Conothele Thorell, 1878 collected from China are described as new to science based on the female genital morphology: C.baisha sp. n. (Hainan Province), C.baoting sp. n. (Hainan Province), C.linzhi sp. n. (Tibet), and C.jinggangshan sp. n. (Jiangxi Province). For two Hainan species, C.baisha sp. n. and C.baoting sp. n., between which it is difficult to distinguish solely based on female genital morphology, additional diagnoses derived from species-specific nucleotide substitution information and genetic distances using the mitochondrial gene, cytochrome c oxidase subunit I are provided.

Two new species of the purse-web spider genus Atypus Latreille, 1804 from Hainan Island, China (Araneae, Atypidae).

Two species of the purse-web spider genus Atypus Latreille, 1804 collected from Hainan Island, China, are diagnosed and described as new to science based on genital morphology, A. baotingensissp. n. (♂♀) and A. jianfengensissp. n. (♀). The DNA barcodes of the two species are also provided for future use.

Four new species of the trapdoor spider genus Conothele Thorell, 1878 from Mainland China and Laos (Araneae, Ctenizidae).

Here for the first time the presence of the trapdoor spider genus Conothele Thorell, 1878 (Araneae: Ctenizidae) is reported from mainland China and Laos. Four Conothele species collected from the regions are described as new to science, based on the female genital morphology: Conothele baiyunensis Xu, Xu & Liu, sp. n. (Guangdong Province), Conothele daxinensis Xu, Xu & Li, sp. n. (Guangxi Province), Conothele sidiechongensis Xu, Xu & Liu, sp. n. (Yunnan Province, China and Vietnam), Conothele yundingensis Xu, Xu & Li, sp. n. (Yunnan Province).